Semiconductor memory is widely used in various electronic devices such as cellular telephones, digital cameras, personal digital assistants, medical electronics, mobile computing devices, and non-mobile computing devices. Semiconductor memory may comprise non-volatile memory or volatile memory. A non-volatile memory allows information to be stored and retained even when the non-volatile memory is not connected to a source of power (e.g., a battery).
One example of non-volatile memory uses reversible resistance-switching memory elements that may be set to either low or high resistance states. Upon application of sufficient voltage, current, or other stimulus, the reversible resistance-switching memory element switches to a stable low-resistance state, which is sometimes referred to as SETTING the device. This resistance-switching is reversible such that subsequent application of an appropriate voltage, current, or other stimulus can serve to return the reversible resistance-switching material to a stable high-resistance state, which is sometimes referred to as RESETTING the device. This conversion can be repeated many times.
Three dimensional (“3D”) memory arrays having reversible resistance-switching memory elements have been proposed. In one possible architecture, word lines extend horizontally and bit lines extend vertically. There a multiple levels of the word lines, hence multiple levels of memory elements. Each memory element is located between one of the vertical bit lines and one of the horizontal word lines. During operation, some of the memory cells are selected for the SET or RESET, while others are unselected.
As some memory systems are used in portable electronic devices that utilize batteries, conserving power is a goal.